Abstract [en]

The UHF band is often used for communication over water. Presented work quantifies path loss for this scenario. Experimental results are presented within 200 MHz to 1000 MHz, with the antennas positioned up to 2 m above the water surface. Path loss models are created from the measured data.

Ödman, Torbjörn

Abstract [en]

This licentiate thesis presents an advanced wireless system, built on a single hardware platform, for applications in medicine and health. In order to design a single system, adaptable for different context, an accurate system specification is required.

The technical requirements are authenticated by actual tests in the environment where the system is intended to be used. The results of these measurements give an understanding of the possibilities of designing a real system but also acts as a base for deriving the empirical formulas to be used as the basis of the development and verification.

In summary, this work has included a larger measurement campaign and a verification of subsystems to support the development of wireless systems on a single hardware platform. This can be used for different measurements in medical healthcare and rescue work.

Previous systems for endurance tests have limitations in that they are not adapted to different sizes of mammals and they also have shortcomings in the quantification of data and scalability.

The developed system was validated on mice and humans. On mice the measurement parameters was the hormone dopamine and locomotion. For humans it was measured time for given distances. Both validation tests showed high correlation with the respective reference methods. The correlation coefficients of mice between the developed system and the former system ranged from 0.916 to 0.967. In the validation with humans, runners were clocked by the system clock and a manual stop watch. The lowest correlation coefficient was 0.864. Advantages with the developed system is that it is scalable and measures the activity level quantitatively in the unit meters and it can also be used for different sizes of mammals in different environments.

In tracking devices for rescue it is important that the transmitted signal can be detected at distances as large as possible. A support in the design work is to simulate path loss. This requires a path loss exponent, which was calculated after the measurement campaign. The results showed that the exponent of the height dependency decreases with antenna height above water. For the frequency 200 MHz, the exponent for the antenna height is 0.4 (vertical polarization) and 1.5 (horizontal polarization). For the distance dependency, the exponent was 3.59 (vertical polarization) and 3.22 (horizontal polarization). The path loss exponent is 2 for both the free space- and the ground reflection model.

An antenna’s physical dimension is to a large extent dependent on the lowest frequency. The research’s aim was to reduce the physical size by introducing a resonance frequency. The physical length was from the beginning 0.43 meter given by the lowest frequency used (0.7 GHz) and the antenna was reduced in size to 0.22 meter.